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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        // 声明并赋值
        let age = 20
        console.log('@@@age', age);
        // 变量值更新
        age = 30
        console.log('@@@age', age);
    </script>
</body>
</html>